This application relates to semiconductor III-V alloy compounds and more particularly to a method of making III-V alloy compounds for use in diode lasers.
The growth of semiconductor III-V compounds by chemical vapor deposition (CVD) using organometallics and hydrides as elemental sources has developed into a viable process with many potential commercial applications. The metallo-organic chemical vapor deposition (MOCVD) process, based on the pyrolysis of alkyls of group-III elements in an atmosphere of the hydrides of group-V elements, is a common growth technique because it is well adapted to the growth of submicron layers and heterostructures.
Open-tube flow systems are used at atmospheric or reduced pressures in producing the III-V alloys. The process requires only one high-temperature zone for the in situ formation and growth of the semiconductor compound directly on a heated substrate.
Low pressure (LP-) MOCVD growth method offers an improved thickness uniformity and compositional homogeneity, reduction of autodoping, reduction of parasitic decomposition in the gas phase, and allows the growth of high-quality material over a large surface area. The LP-MOCVD technique has been successfully used to grow GaxIn1xe2x88x92xAsyP1xe2x88x92y (0xe2x89xa6xxe2x89xa60.47 and 0xe2x89xa6yxe2x89xa61) lattice matched to InP for the complete compositional range between InP (xcex=0.91 xcexcm, Eg=1.35 eV) and the ternary compound Ga0.47In0.53As (xcex=1.67 xcexcm, Eg=0.75 eV). GaInAsP alloys, which are potentially useful materials both for heterojunction microwave and optoelectronic device applications can be grown by liquid-phase epitaxy (LPE), molecular-beam epitaxy (MBE), conventional vapor-phase epitaxy (VPE), as well as MOCVD.
The technique of LP-MOCVD is well adapted to the growth of the entire composition range of GaInAsP layers of uniform thickness and composition that is lattice matched to GaAs over areas of more than 10 cm2. This results first from the ability of the process to produce abrupt composition changes and second from the result that the composition and growth rate are generally temperature independent. It is a versatile technique, numerous starting compounds can be used, and growth is controlled by fully independent parameters.
Growth by MOCVD takes place far from a thermodynamic equilibrium, and growth rates are determined generally by the arrival rate of material at the growing surface rather than by temperature-dependent reactions between the gas and solid phases. In contrast to LPE growth, it has been found that during MOCVD growth of a double heterostructure, GaAs can be grown directly on GaInAsP with no disturbance of the active layer, i.e., there is no effect equivalent to melt-back. One of the key reasons for the usefulness of this method is the possibility of obtaining high-purity and therefore high-mobility GaxIn1xe2x88x92xAsyP1xe2x88x92y. As long-wavelength 1.0-1.65 xcexcm GaInAsP electro-optical devices become more widely used, motivated by low fiber absorption and dispersion, high transmission through water and smoke, and greatly enhanced eye safety at wavelengths greater than 1.4 xcexcm, LP-MOCVD offers the advantages of smooth uniform surfaces, sharp interfaces (lower than 5 xc3x85 for GaInAsP/GaAs), uniformly lower background doping density, and economy of scale for large-area devices.
Recent studies have shown the feasibility of using InGaAsP/GaAs heterostructures as diode lasers. The diodes can be used successfully for solid state laser pumping and can be interchanged with lasers based on AlGaAs/GaAs heterostructures.
A feature, therefore, of the invention is the growth of high quality GaxIn1xe2x88x92xAsyP1xe2x88x92y (xcex between 700 up to 1100 nm)=808 nm)/GaAs GRIN-SCH (Graded Index Separate Confinement) double heterostructures by either low-pressure metallorganic chemical vapor deposition (LP-MOCVD) or gas source MBE.
A further feature of the subject invention is a double heterojunction laser structure grown with strained layer quantum wells.
A still further feature of the subject invention is a method of controlling the wavelength range and energy gap of the diode laser by varying both the composition of the strained layer quantum wells.
Another feature of the subject invention is a method of changing the wavelength by changing the Ga, In, Al P and As sources to vary the composition of the resulting heterojunction composition.
A still further features of the subject invention is a method of doping a contact layer of a heterostructure for use in a diode laser so as to include a high volume percentage of dopant atoms in the surface.
These and other features are attained by the subject invention wherein SCH-SQW (separate confinement heterostructure, single quantum well) diode lasers of the formula GaInP/InGaAsP on GaAs substrates with waveguides of AlGaAs, operating at powers higher than 5W with emitting apertures of 100 microns are prepared. By varying compositions and by employing strained layer quantum wells, lnGaAsP diode lasers can be fabricated over the wavelength range of 700 to 1100 nm.